The present invention relates to a control method of an AC motor by which a speed of the AC motor is varied by a variable speed control apparatus to output the AC voltage, and specially to a control method and an apparatus by which the AC motor can be smoothly started after the return from the power failure.
Conventionally, to speed control the AC motor, a V/f constant control method by which a ratio of the output voltage V and an output frequency f is made constant, is well known. Further, recently, in order to more accurately control the AC motor, a vector control to respectively independently control the primary current to be supplied to the AC motor, in the exciting current (current to generate the magnetic flux) and the torque current (current to generate the torque) which directly relate to the torque, is brought into the practical use. However, in the conventional control system, during the continuous running, the stable control is conducted, however, in the case where the instantaneous power failure is generated in the running of the AC motor once, and restarting after the instantaneous power failure is conducted, when the residual voltage of the AC motor and the phase of the voltage command of the variable speed control apparatus are not matched, the speed of the AC motor is rapidly changed, or a slip of the AC motor is increased, thereby, the over current flows, resulting in a danger such as a trip. In order to prevent this, it is necessary that the residual voltage of the AC motor and the phase of the voltage command of the variable speed control apparatus are matched, and the re-running is conducted, however, the matching of the phase is very difficult. Therefore, because, after the residual voltage does not exist, the angular velocity of the AC motor and the output frequency of the variable speed control apparatus are calculated from the speed detector, or the residual voltage of the AC motor is detected by the voltage detector, and by being calculated from its frequency component, the phases of the residual voltage and the output voltage command signal are made to coincide with each other, and re-running is conducted, there is a problem that the restart after the instantaneous power failure takes a long period of time, or a smooth re-running is difficult.
As described above, in order to smoothly start the AC motor, there is a problem that it is necessary to wait that the residual voltage does not exist, or the detector such as the speed detector or voltage detector is necessary.
Accordingly, the object of the present invention is to provide the control method and control apparatus of the AC motor by which, by accurately measuring the phase and angular velocity of the residual voltage of the AC motor after the recovery of the instantaneous power failure, the re-running can be quickly and smoothly conducted.
The summary of a control method and control apparatus of the AC motor of the present invention to solve the above problem, exists in the following (1) to (23).
(1) A control method of an AC motor which is characterized in that: it has an electric power converter to output the electric power to the AC motor, and is provided with a current control section to control the output current of the electric power converter based on the difference signal of the current command signal and the output current detection signal of the electric power converter, and when the AC motor is in a free run condition, the current command signal is forcibly made zero so that the current of the AC motor is made zero, and current controlled, and on the base of the output voltage command signal which is calculated by using the current control section output at this time, the amplitude and phase and angular velocity of the residual voltage of the AC motor are obtained.
(2) A control method of an AC motor according to (1), wherein, when the phase and the angular velocity of the residual voltage of the AC motor are obtained based on the output voltage command signal, a signal holding means is provided, and the amplitude, and phase and angular velocity of the residual voltage are obtained from the addition value of the phase command signal just before the AC motor free runs, and the phase signal of the output voltage command signal.
According to this control method of the AC motor, in the case where the AC motor is in the free run condition, when it is controlled so that the current of the AC motor becomes zero, it is utilized as this result that the residual voltage of the AC motor appears in the voltage command signal, the amplitude and phase and angular velocity of the residual voltage of the AC motor which is in the free run condition, are obtained on the base of the phase and angular frequency of the this voltage command signal. Thereby, the smooth speed-return after the power failure recovery becomes easy.
Further, when the phase and angular velocity of the residual voltage are searched, a signal holding means is provided, and because the phase and angular velocity of the residual voltage are searched from the addition value of the phase command signal and the phase signal of the output voltage command signal just before the AC motor free-runs, there is no discontinuity of the phase command signal and a disadvantage such as the mechanical shock occurrence can be prevented.
(3) A control method of an AC motor which is characterized in that: in the control method by which an arbitrary electric power is outputted to the AC motor by the electric power converter, and the current supplied to the motor is detected by the current detection circuit, and it is controlled by the current control circuit so that the given current command and the current detection value detected by the current detection circuit coincide to each other, and the switching of the electric power converter is determined from the voltage command outputted from the current control circuit, the electric power converter is controlled by a start control circuit so that it is normally operated at the start time, and the speed of the AC motor in the free run condition is estimated by a speed estimation circuit.
(4) A control method of an AC motor according to (3), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command so that the current detection value is made zero, is calculated, and by the time change of the voltage command, the speed estimation circuit estimates the speed of the AC motor.
(5) A control method of an AC motor according to either one of (3) or (4), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when its voltage level is lower than the set voltage level, after the set-level DC current command is applied for a set time period from zero, the current command is forcibly made zero again, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and the speed estimation circuit estimates the speed of the AC motor.
(6) A control method of an AC motor according to any one of (3) to (5), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when its voltage level is lower than the set voltage level, after the set level DC current command is applied for a set time period from zero, the current command is forcibly made zero again, and by the current control circuit, even when the voltage command by which the current detection value is made zero, is calculated, when that voltage level is lower than the set voltage level, the speed estimation circuit estimates that the AC motor is stopped.
(7) A control method of an AC motor according to any one of (1) to (6), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command so that the current detection value is made zero, is calculated, and by the time change of the voltage command, the speed estimation circuit starts the AC motor when the estimated AC motor speed and the amplitude and the phase of the voltage command are made the initial value.
(8) A control method of an AC motor according to any one of (1) to (7), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command so that the current detection value is made zero, is calculated, and by the time change of the voltage command, when the speed estimation circuit starts the AC motor when the estimated AC motor speed and the amplitude and the phase of the voltage command are made the initial value, until the amplitude of the voltage command outputted from the electric power converter is brought into the voltage level corresponding to the normal induced voltage to the speed of the AC motor, the voltage command is gradually increased.
(9) A control apparatus of an AC motor which is characterized in that: in the control apparatus of the AC motor which has the electric power converter to output an arbitrary electric power to the AC motor; the current detection circuit by which the current supplied to the motor is detected; the current control circuit to control so that the given current command and the current detection value detected by the current detection circuit coincide with each other; and by which the switching of the electric power converter is determined from the voltage command outputted from the current control circuit, the apparatus has the start control circuit, and the speed estimation circuit by which the speed of the AC motor in the free run condition is estimated.
(10) A control apparatus of an AC motor according to (9), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command so that the current detection value is made zero is calculated, and by the time change of the voltage command, the speed estimation circuit estimates the speed of the AC motor.
(11) A control apparatus of an AC motor according to either one of (9) or (10), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command so that the current detection value is made zero is calculated, and when its voltage level is lower than the set voltage level, after the set level DC current command is applied for a set time period from zero, the current command is forcibly made zero again, and by the current control circuit, the voltage command so that the current detection value is made zero, is calculated, and the speed estimation circuit estimates the speed of the AC motor.
(12) A control apparatus of an AC motor according to any one of (9) to (11), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command so that the current detection value is made zero is calculated, and when its voltage level is lower than the set voltage level, after the set level DC current command is applied for a set time period from zero, the current command is forcibly made zero again, and by the current control circuit, even when the voltage command so that the current detection value is made zero, is calculated, when its voltage level is lower than the set voltage level, the speed estimation circuit estimates that the AC motor is stopped.
(13) A control apparatus of an AC motor according to any one of (9) to (12), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and by the time change of the voltage command, the speed estimation circuit makes the estimated speed of the AC motor and the amplitude and phase of the voltage command the initial value, and starts the AC motor.
(14) A control apparatus of an AC motor according to any one of (9) to (13), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and by the time change of the voltage command, when the speed estimation circuit makes the estimated speed of the AC motor and the amplitude and phase of the voltage command the initial value, and starts the AC motor, the amplitude of the voltage command outputted from the electric power converter is gradually increased up to the voltage level corresponding to the normal induced voltage to the speed of the AC motor.
(15) A control method of an AC motor according to (3), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when the voltage command is larger than the set voltage level, by the time change of the phase of the voltage command, the speed estimation circuit estimates the speed of the AC motor, and as the initial value when the electric power converter is started, the amplitude and phase of the voltage command and the frequency corresponding to the speed estimation value of the AC motor are set, and the electric power converter is started.
(16) A control method of an AC motor which is characterized in that: the apparatus has an electric power converter to output the electric power to the AC motor; the current control section to control the output current of the electric power converter based on the difference signal of the current command signal and the output current detection signal of the electric power converter; and when the AC motor is in the free run condition, the arbitrary DC current is supplied to the AC motor for a set time period, and the frequency component appeared in the output current detection signal of the electric power converter is detected, and from the frequency component, the speed of the AC motor is estimated.
(17) A control method of an AC motor according to (3), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when its voltage level is lower than the set voltage level, the set level DC current command or the set level DC voltage command is applied for a set time period from zero, and the speed estimation circuit detects the frequency component appeared in the current detection value, and this frequency component is estimated as the speed of the AC motor, and as the initial value when the electric power converter is started, the frequency corresponding to the speed estimation value of the AC motor is set, and the electric power converter is started.
(18) A control method of an AC motor according to (3), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when the voltage command is lower than the set voltage level, the current command value is changed from zero to the set level DC current command value, and this is applied for a set time period, and after that, the sign and amplitude of the current command are changed, and it is applied for a set time period. A control method of an AC motor is characterized in that, at this time, the speed estimation circuit detects the frequency component appeared in the current detection value, and it estimates the frequency component as the speed of the AC motor, and as the initial value when the electric power converter is started, the frequency corresponding to the speed estimation value of the AC motor is set, and the electric power converter is started.
(19) A control method of an AC motor according to (3), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when the voltage command is lower than the set voltage level, the current control is stopped, and the DC voltage command is applied in the arbitrary direction for a set time period, and after that, the arbitrary amplitude current command is given in the direction in which the phase is changed by 180xc2x0 from the command direction of the DC voltage, and the current control is conducted again for a set time period. A control method of an AC motor characterized in that, at this time, the speed estimation circuit detects the frequency component appeared in the current detection value, and estimates the frequency component as the speed of the AC motor, and as the initial value when the electric power converter is started, the frequency corresponding to the speed estimation value of the AC motor is set, and the electric power converter is started.
(20) A control apparatus of an AC motor according to (9), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when the voltage command is larger than the set voltage level, by the time change of the phase of the voltage command, the speed estimation circuit estimates the speed of the AC motor, and as the initial value when the electric power converter is started, the amplitude and phase of the voltage command and the frequency corresponding to the speed estimation value of the AC motor are set, and the electric power converter is started.
(21) A control apparatus of an AC motor according to (9), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when the voltage command is lower than the set voltage level, the set level DC current command, or the set level DC voltage command is applied for a set time period from zero, and the speed estimation circuit detects the frequency component appeared in the current detection value, and estimates the frequency component as the speed of the AC motor, and as the initial value when the electric power converter is started, the frequency corresponding to the speed estimation value of the AC motor is set, and the electric power converter is started.
(22) A control apparatus of an AC motor according to (9), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when the voltage command is lower than the set voltage level, the current command value is changed from the zero to the set level DC current command vale, and it is applied for a set time period, and after that, the sign and the amplitude of the current command are changed, and applied for a set time period. The control apparatus of the AC motor is characterized in that, at this time, the speed estimation circuit detects the frequency component appeared in the current detection value, and estimates the frequency component as the speed of the AC motor, and as the initial value when the electric power converter is started, the frequency corresponding to the speed estimation value of the AC motor is set, and the electric power converter is started.
(23) A control apparatus of an AC motor according to (3), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when the voltage command is lower than the set voltage level, the current control is stopped, and the DC voltage command is applied in the arbitrary direction for a set time period, and after that, the arbitrary amplitude current command is given in the direction in which the phase is changed by 180xc2x0 from the command direction of the DC voltage, and the current control is conducted again for a set time period. The control apparatus of the AC motor characterized in that, at this time, the speed estimation circuit detects the frequency component appeared in the current detection value, and estimates the frequency component as the speed of the AC motor, and as the initial value when the electric power converter is started, the frequency corresponding to the speed estimation value of the AC motor is set, and the electric power converter is started.